Feasibility of 3D Printing on Environmentally Friendly Cementless Materials with Low Thermal Conductivity

To achieve the goal of construction automation, the application of 3D printing technology in construction is a significant development trend in the future. 3D printing has the advantages of high precision, high speed, low cost, and environmental protection. It can help reduce construction costs and reduce time and energy. In addition, it can also be used to construct complex shapes that would otherwise be difficult to achieve. To achieve the goal of a circular economy, this study utilized different types of industrial by-products (co-fired fly ash, ultra-fine fly ash, fly ash and ground granulated blast-furnace slag) to produce ternary cementless colloidal without alkali activators. It was also used as a low-carbon alternative to traditional cement. Furthermore, the use of by-products reduced the environmental impact of production. This study used a paste-type 3D printer with model number UM 2205. Set time, fluidity, mini-slump and compressive strength were used to verify the constructability of the 3D-printed specimens. The test results showed that 3D-printed paste specimens mixed with 60% slag, 30% co-fired fly ash and 10% fly ash had the highest compressive strength. The 28-day compressive strength reached 25 MPa and was better than steel-molded specimens. The remaining ternary cementless printed specimens achieved a compressive strength of 15-20 MPa. However, the strength of the printed specimens was lower than that of the steel molded specimens. The cementitious properties of cementless colloidal materials were analyzed by scanning electron microscope observations and XRD tests. In the microstructures of these printed specimens, needle-like hydration reactions were clearly visible, which were hydrations such as C-A-S-H or ettringite, which also provided cementless materials with strength. The gaps between the printed layers were complete and the cross-section was filled without large air bubbles as observed by an optical microscope. The hydration products created a dense microstructure within the printed specimens, increasing strength and permeability. The study showed that 3D printing effectively made cementless materials with improved strength and durability.

In this study, three industrial by-products (ultrafine fly ash, ground granulated blast-furnace slag (ggbs) and circulating fluidized bed co-fired fly ash) were used to produce ternary cementless composites without using alkali activators. The finenesses of ultrafine fly ash, ggbs and co-fired fly ash were 33,800, 5830 and 5130 cm2/g, respectively. The composite material was developed by mixing supplementary cementing materials of different particle sizes and exploiting the high-alkaline properties of the co-fired fly ash to develop a substantial hardening property like cement. The test specimens were made in the form of pastes and the water-to-cementitious-material ratio for the test was fixed at 0.55. The test results show that the flowability of the six different mixtures could be up to 120% and the setting time could be controlled within 24 h. At 60% of the ggbs proportion, the setting time could be held for 8 h. The compressive strength of each proportion reached 7 MPa at 7 days and 14 MPa at 28 days. The water-cured specimens exhibited better strength behavior than the air-cured specimens. Scanning electron microscopy found the main components of strength growth of the specimens to be hydrated reactants of C-A-S-H or ettringite. The results of the XRF analysis show that the specimens responded to higher compressive strengths as the Ca/Si and Ca/Al ratios increased.

The effect of ultrafine fly ash (UFA) and fly ash (FA) on the physical properties, phase assemblage, and microstructure of magnesium potassium phosphate cement (MKPC) was investigated. This study revealed that the UFA addition does not affect the calorimetry hydration peak associated with MKPC formation when normalized to the reactive components (MgO and KH2PO4). However, there is an indication that greater UFA additions lead to an increased reaction duration, suggesting the potential formation of secondary reaction products. The addition of a UFA:FA blend can delay the hydration and the setting time of MKPC, enhancing workability. MgKPO4·6H2O was the main crystalline phase observed in all systems; however, at low replacement levels in the UFA-only system (<30 wt %), Mg2KH(PO4)2·15H2O was also observed by XRD, SEM/EDS, TGA, and NMR (31P MAS, 1H-31P CP MAS). Detailed SEM/EDS and MAS NMR investigations (27Al, 29Si, 31P) demonstrated that the role of UFA and UFA:FA was mainly as a filler and diluent. Overall, the optimized formulation was determined to contain 40 wt % fly ash (10 wt % UFA and 30 wt % FA (U10F30)), which achieved the highest compressive strength and fluidity and produced a dense microstructure.

Low thermal conductivity materials are now an essential direction for construction material applications as the public has become more aware of global warming over the past few years. The development of cementless binders is also helping to improve the problem of global warming. This study uses reactive ultra-fine fly ash (RUFA) and co-fired fly ash (CFA) to develop an innovative cementless binder. The RUFA-CFA mixture undergoes hardening without alkali activators at a temperature of 50 °C before it is de-molded for air curing. The resulting lightweight cementless specimens present excellent thermal insulation, mainly due to the formation of interstitial pores between RUFA particles. The porosity of RUFA-CFA cementless specimens ranges from 41% to 50% with minimum thermal conductivity of 0.10 W/m·K. Our analysis reveals that the ultra-fine RUFA particles adhere to the CFA surface formed C-S-H colloids and ettringite via continuous hydrated reactions maintained by the CFA. The results obtained in this study provide a valuable reference for developing cementless composites based on industrial waste materials.

This paper evaluates the effect of Ultrafine Fly Ash (UFFA) and nanoSilica (NS) on compressive strength of high volume fly ash (HVFA) mortar at 7 days and 28 days. Three series of mortar mixes are considered in the first part of this study. In the first series the effect of high content of class F fly ash as partial replacement of cement at 40, 50 and 60% (by wt.) are considered. While in the second and third series, the UFFA and NS are used as partial replacement of cement at 5%, 8%, 10%, 12% and 15% and 1%, 2%, 4%, 6% and 8% (by wt.) of cement, respectively. The UFFA and the NS content which exhibited highest compressive strength in the above series are used in the second part where their effects on the compressive strength of HVFA mortars are evaluated. Results show that the mortar containing 10% UFFA as partial replacement of cement exhibited the highest compressive strength at both 7 and 28 days among all UFFA contents. Similarly, the mortar containing 2% NS as partial replacement of cement exhibited the best performance. Interestingly, the use of UFFA in HVFA mortars did not improve the compressive strength. However, the use of 2% and 4% NS showed improvement in the compressive strength of HVFA mortar containing 40% and 50% fly ash at both ages. The effects of NS and UFFA on the hydration and strength development of HVFA mortar is also evaluated through X-Ray Diffraction (XRD) test. Results also show that the UFFA and NS can significantly reduce the calcium hydroxide (CH) in HVFA mortars.

This study aims to investigate the binding properties of co-fired fly ash (CFFA) in paste and mortar specimens. Paste specimens containing various CFFA proportions (25%, 50%, 75%, 100% by weight of cement) were conducted and evaluated using setting time tests, water demand tests and compressive strength tests. Mortar specimens containing various CFFA and Pulverised coal fly ash (PCFA) proportions (10%, 20%, 30% by weight of cement) were also conducted and compared with regard to flowability and compressive strength. The test results indicated that the water demand increased as the amount of CFFA replacement increased on the flow level at 110±3%; this is due to the higher ignition loss (L.O.I.). Higher L.O.I. values mean that there are more unburned carbon particles in the CFFA and that most of these carbon particles are porous. The compressive strength of mortar specimens decreased as the amount of CFFA replacement increased. Compared to the chemical compositions of cement (C3S, C2S), the main components of CFFA (Ca(OH)2, CaCO3, CaO) have lower crystalline strength and compactness. Therefore, the higher amount of CFFA replacement would inevitably cause a reduction of the cement contents of specimens, thereby reducing the compressive strength of the mortar specimens. Thus, an appropriate amount of superplasticiser and CFFA replacement in the mixture is useful with regard to the binding properties of cementitious materials.

Compressive strength and durability properties of high volume fly ash (HVFA) concretes containing ultrafine fly ash (UFFA)

Research on properties evolution of ultrafine fly ash and cement composite

The research aims to address waste-related issues by producing Cellular Lightweight Concrete (CLC) bricks using fly ash and bottom ash as fine aggregates. The variations used encompass cement, fly ash, bottom ash, and sand compositions. The ratio between cement and fine aggregates utilized is 1:3. The variations in the composition of fine aggregates include P (100% sand), F (100% fly ash), B (100% bottom ash), F1B1 (50% fly ash and 50% bottom ash), F1B2 (33.3% fly ash and 66.7% bottom ash), F1B3 (25% fly ash and 75% bottom ash), F2B1 (6.7% fly ash and 33.3% bottom ash), and F3B1 (25% fly ash and 75% bottom ash). The parameters employed comprise compressive strength testing, density, and water absorption evaluation of the CLC bricks at ages 14, 28, and 35 days, also thermal conductivity at the 35-days sample. The sample age exhibits a proportional relationship with compressive strength and water absorption, while displaying an inverse relationship with density. At the 35-day sample age, the F composition demonstrates the highest compressive strength (14.74MPa) and the lowest water absorption (11%). Meanwhile, the B composition exhibits a compressive strength value of 5.9MPa and the lowest density (1.12g/cm2). Conversely, the P composition showcases the highest density (1.59g/cm2). Density affects thermal conductivity, the lower the density, the lower the thermal conductivity, which means that the heat conductivity will be smaller.

Study on the cementation and engineering properties of ternary eco-binder mortar containing pulverized coal fly ash mixed with circulating fluidized bed co-fired fly ash

Effect of ultrafine fly ash on mechanical properties of high volume fly ash mortar

Influence of steam curing on the compressive strength of concrete containing supplementary cementing materials

In this study, mechanical activation is used to generate ultra-fine fly ash (UFA) for high volume fly ash（FA）cement composites. The effects of different content and medium particle size of FA on mortar`s electrical resistivity, chloride penetration and mechanical properties are investigated. The results show that the compressive strength and resistance to chloride permeability of specimens with UFA have been enhanced, owing to higher pozzolanic reaction and higher dissolution rate of Si and Al units of UFA to accelerate the generate of reaction products. However, At the early ages, electrical resistivity of specimens increases with the increase of UFA; at later ages, specimens have a higher electrical resistivity with the increase of UFA.

Effect of steam curing on compressive strength and microstructure of high volume ultrafine fly ash cement mortar

This paper is aimed to study the rheological and physical performance of mortars manufactured replacing Portland-based cements with low calcium siliceous fly ash (FA) or ultrafine fly ash (UFFA). Five different types of cement (CEM I, CEM II/A-LL, CEM III/A, CEM III/B, and CEM IV according to EN 197-1) were used. Mortars were manufactured with FA or UFFA replacing 5%, 15%, 25%, 35%, and 50% of cement mass. Results indicate that compressive strength of mortars with UFFA is considerably higher than that of mixtures containing traditional FA, both at early and long ages. Moreover, experimental data reveal that replacement of cement with up to 25% of UFFA determines higher compressive strength at 7, 28, and 84 days than plain mortars (containing cement only), regardless of the type of cement used. Mortars manufactured with 35% or 50% of UFFA show slightly lower or similar compressive strength compared to the reference mortar (containing cement only). In addition, the results show values of the strength activity index of mortars made with FA 25%, 23%, and 20% lower than the reference corresponding mortars (cement only) at 7, 28, and 84 days, respectively. The grinding of FA, despite resulting in an increase in production energy and CO2 emissions compared to unmilled FA, allows a wide use of these SCM (Supplementary Cementitious Materials) in place of cement, reducing the environmental impact of mortars up to 40% at the 28-day strength class. The use of UFFA ensures better resistance in CaCl2-rich environments.